Hi,
A number of instructions are output in assembler form by
output_return_instruction () when compiling a function with the
cmse_nonsecure_entry attribute for Armv8-M Mainline with hardfloat float
ABI. However, the corresponding thumb2_cmse_entry_return insn pattern
does not account for all these instructions in its computing of the
length of the instruction.
This may lead GCC to use the wrong branching instruction due to
incorrect computation of the offset between the branch instruction's
address and the target address.
This commit fixes the mismatch between what output_return_instruction ()
does and what the pattern think it does and adds a note warning about
mismatch in the affected functions' heading comments to ensure code does
not get out of sync again.
Note: no test is provided because the C testcase is fragile (only works
on GCC 6) and the extracted RTL test fails to compile due to bugs in the
RTL frontend (PR82815 and PR82817)
ChangeLog entries are as follows:
*** gcc/ChangeLog ***
2017-10-30 Thomas Preud'homme <thomas.preudho...@arm.com>
* config/arm/arm.c (output_return_instruction): Add comments to
indicate requirement for cmse_nonsecure_entry return to account
for the size of clearing instruction output here.
(thumb_exit): Likewise.
* config/arm/thumb2.md (thumb2_cmse_entry_return): Fix length for
return in hardfloat mode.
Testing: Bootstrapped on arm-linux-gnueabihf and testsuite shows no
regression.
Is this ok for trunk?
Best regards,
Thomas
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 033ec255a577f782201527f57f45802bc0eb45e0..9919f54242d9317125a104f9777d76a85de80e9b 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -19417,7 +19417,12 @@ arm_get_vfp_saved_size (void)
/* Generate a function exit sequence. If REALLY_RETURN is false, then do
everything bar the final return instruction. If simple_return is true,
- then do not output epilogue, because it has already been emitted in RTL. */
+ then do not output epilogue, because it has already been emitted in RTL.
+
+ Note: do not forget to update length attribute of corresponding insn pattern
+ when changing assembly output (eg. length attribute of
+ thumb2_cmse_entry_return when updating Armv8-M Mainline Security Extensions
+ register clearing sequences). */
const char *
output_return_instruction (rtx operand, bool really_return, bool reverse,
bool simple_return)
@@ -23950,7 +23955,12 @@ thumb_pop (FILE *f, unsigned long mask)
/* Generate code to return from a thumb function.
If 'reg_containing_return_addr' is -1, then the return address is
- actually on the stack, at the stack pointer. */
+ actually on the stack, at the stack pointer.
+
+ Note: do not forget to update length attribute of corresponding insn pattern
+ when changing assembly output (eg. length attribute of epilogue_insns when
+ updating Armv8-M Baseline Security Extensions register clearing
+ sequences). */
static void
thumb_exit (FILE *f, int reg_containing_return_addr)
{
diff --git a/gcc/config/arm/thumb2.md b/gcc/config/arm/thumb2.md
index b78c3d256aeafc2eeb3dcdc2b9b07b1af9df5294..776d611d2538e790a5f504995050ffdfc51d7193 100644
--- a/gcc/config/arm/thumb2.md
+++ b/gcc/config/arm/thumb2.md
@@ -1132,7 +1132,7 @@
; we adapt the length accordingly.
(set (attr "length")
(if_then_else (match_test "TARGET_HARD_FLOAT")
- (const_int 12)
+ (const_int 34)
(const_int 8)))
; We do not support predicate execution of returns from cmse_nonsecure_entry
; functions because we need to clear the APSR. Since predicable has to be
